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arXiv 1406.3071astro-ph.GAastro-ph.HE
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来自几乎没有分子气体的尘埃区的两个伽马射线暴

Two gamma-ray bursts from dusty regions with little molecular gas

B. Hatsukade, K. Ohta, A. Endo, K. Nakanishi, Y. Tamura, T. Hashimoto, K. Kohno

摘要:

持续时间长的伽马射线暴与大质量恒星的爆炸有关,因此被认为存在于有分子气体(恒星形成的燃料)的恒星形成区域。以前在爆发的宿主星系中寻找一氧化碳(CO),一种分子气体的示踪剂,没有检测到任何排放。在伽马射线暴余辉的光谱中,分子被探测为吸收,分子气体类似于银河系中半透明或弥漫的分子云。吸收线只沿着视线探测星际介质,因此尚不清楚分子气体是否代表爆发发生区域的一般性质。在这里,我们报告的空间分辨观测CO线发射和毫米波长的连续发射在两个星系托管伽马射线暴。爆发发生在富含尘埃的区域,但分子气体并不特别丰富。分子气体与尘埃的比例(<9-14)明显低于银河系和附近恒星形成星系的恒星形成区,这表明恒星形成的大部分致密气体已经被其他大质量恒星消散。

英文摘要:

Long-duration gamma-ray bursts are associated with the explosions of massive stars and are accordingly expected to reside in star-forming regions with molecular gas (the fuel for star formation). Previous searches for carbon monoxide (CO), a tracer of molecular gas, in burst host galaxies did not detect any emission. Molecules have been detected as absorption in the spectra of gamma-ray burst afterglows, and the molecular gas is similar to the translucent or diffuse molecular clouds of the Milky Way. Absorption lines probe the interstellar medium only along the line of sight, so it is not clear whether the molecular gas represents the general properties of the regions where the bursts occur. Here we report spatially resolved observations of CO line emission and millimetre-wavelength continuum emission in two galaxies hosting gamma-ray bursts. The bursts happened in regions rich in dust, but not particularly rich in molecular gas. The ratio of molecular gas to dust (<9-14) is significantly lower than in star-forming regions of the Milky Way and nearby star-forming galaxies, suggesting that much of the dense gas where stars form has been dissipated by other massive stars.

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